Device for clamping screen frames in sifters



Nov. 15, 1955 w. c. CONKLING ,723.

DEVICE FOR CLAMPING SCREEN FRAMES IN SIFTERS Filed Sept. 27, 1950 I5 Sheets-Sheet l INVEN TOR.

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v BYMC rp- MM Nov. 15, 1955 w. c. CONKLING 2,723,751

DEVICE FOR CLAMPING SCREEN FRAMES IN SIFTERS Filed Sept. 27, 1950 3 Sheets-Sheet 2 dd c 7 @1 Hornegs.

NOV. 15, 1955 w. c, CONKLING 2,723,751

DEVICE FOR CLAMPING SCREEN FRAMES IN SIFTERS Filed Sept. 27. 1950 3 Sheets-Sheet 5 we CI'NV EN TOR. BY w.

United States Patent DEVICE FOR CLAMPING SCREEN FRAMES IN SIFTERS William C. Conkling, Lockport, :N. Y., assignor to Richmond Manufacturing Company, Lockport, N. Y., a corporation of New York Application September 27, 1950, Serial No. 186,959 12 Claims. (Cl. 209-319) This invention relates to. a high speed sitter and more particularly to means for clamping the sides of a stack of rectangular sieves in place in a sitter which is suspended from reeds and which includes an ecentrically weighted rotary shaker for imparting a rotary movement in :a horizontal plane to describe perfect circles of adjustable diameter or amplitude. Features of the invention can be advantageously utilized in sifters other than-the particular type shown, however.

One of the principal objects of the invention is to provide a clamping mechanism for the sides of a stack of sieve frames which, in released condition provides access to one entire side of the stack of sieve frames so that they can be readily removed and replaced in the manner of drawers.

Another object of the invention is toprovide such a clamping mechanism which clamps the four corners of the stack of sieves but isactuated from thatside of the sitter from which thesieves are removed.

Another object is to provide such a clamping mechanism which automatically alines the sieves, individually and as a stack, as it is :tightened and which also exerts clamping pressure on all four corners of the stack and from directions parallel with the sides of the rectangular sieve frames.

Another object is to provide such a clamping mechanism the parts of which remain attached to the sitter atall {times and in operative relation, thereby to facilitate runclamping, changing of sieve frames, .and reclamping the stack.

Another object is to provide such a clamping mechanism which reliably clamps the stack to .the sifter frame without undue strain on the sieve frames, the clamping mechanism or the :sifter frame.

Another object is to provide such ,a clamping .mechanism which is extremely simple in construction and operation and contains few moving parts.

Other objects and advantages of the invention will appear from the following description and drawings in which:

Fig. 1 is a fragmentary perspective view of ahigh speed gyratory sifter having four'stacks of sieves clamped in position by a mechanism embodying the present invention.

Fig. 2 .is a top plan view of the body of the gyratory sifter shown in Fig. 1. r

Fig. 3 is an enlarged fragmentary horizontal section similar to the central part of Fig. '5 and showing a modified form of the invention.

Fig. 4 is a horizontal section similarto Fig. 5 and showing another modifiedform of the invention.

Fig. 5 is an enlarged horizontal section taken generally on line 55, Fig. 1.

Fig. :6 is an enlarged fragmentary side elevational view of the central hinged clamping plate shown in Fig. 1.

Figs. 7, 8 and 9 are horizontal sections taken on the correspondingly numbered lines on Fig.6.

Fig. 10 is a view similar .to the lower left hand corner of Fig. 5 on an enlargedscale andtalso showing the :clamp ing plate in released position.

The main supporting frame for the gyratory sifter is shown as comprising a central framework indicated generally at 20 and including four horizontal cross tubes 21 in rectangular arrangement and extending transversely of the sitter. This central structure is designed to carry the gyratory mechanism (not shown). In each end of each of these tubes 21 is fitted and suitably secured a fitting 22 having a vertical side flange 23 which forms a continuation of the corresponding tube end and is secured to a corresponding vertical corner angle bar 24 which serves .as an abutment bar. The pair of vertical corner angle bars at eachside of the main frame embrace a corresponding pair of stacks 25 of sifter frames 26, as best shown in Fig. 2, and at each side of the main frame these vertical corner angle bars 24 are connected together by a horizontal, tubular side beam 28 which tubular side beams are preferably welded to theseangle bars 24 and are arranged on opposite sides ofthe sifter and preferably are arranged in a horizontal plane intersecting the center of gravity of the sifter. The ends of these horizontal tubular side beams 28 project beyond the vertical corner angle bars 24 and in each end of each of these horizontal tubular side beams 28 is fitted and suitably secured a fitting 29 having a vertical flange 30 which forms a continuation of the corresponding tube end and is secured to a corersponding vertical corner channel bar 31 which also serves as an abutment bar.

At each end of the sifter, the lower ends of the corresponding pair of vertical corner angle bars 24 and pair of vertical corner channel bars 31 carry a rectangular platform 32 for supporting the corresponding pair of sieve stacks 25. Each of these platforms is best shown in Fig. 5 as comprising an inner cross bar 33 extending between the corresponding .pair of vertical corner angle bars 24, an end cross bar 34 between the corresponding pair of vertical corner channel bars .31, bars 35 extending longitudinally of the main sifter body and connecting the ends of the cross bars 33 and 34 and each extending from a corresponding verticalcorner angle bar 24 to the companion vertical corner channel bar 31, and a central bar 36 parallel with the platform bars 35 and connecting the centers of the platform bars 33 and 34.

The main body of the sifter is shown as suspended from four groups of reeds 38 and for this purpose each end of each main longitudinal tubular side bar 28 of the sifter frame has secured .thereto a reed clamp 39 which is clamped to the lower end of the corresponding group of reeds 38. Behind each group of reeds 38 vertical enclosure plates 40 can be provided, the edges of which are preferably secured to the corresponding vertical corner angle bar 24, vertical corner channel bar 31 and platform bar 35. This panel ties the upper ends of the corresponding vertical corner angle bar 24 and the vertical corner channel bar 31 together. The upper ends of the pair of vertical corner channel bars 31 at each end of the sifter frame can be held in proper spaced relation to each other by a .tie rod 41 having each end threaded and extending through an car 42 on the corresponding vertical corner channel bar 31 and provided with a pair of nuts 43 on opposite sides of this ear.

The invention is concerned with the means for clamping the sides of each stack 25 of screen frames 26 on the corresponding platform 32 and to this end, in the form of the invention shown in Figs. 1, 2 and 5-10, 2. vertical spreader angle bar 50 which also forms an abutment bar is secured to each pair of horizontal cross tubes 21 at each end of the sifter at the centers thereof. Each of these vertical spreader angle bars 50 is arranged to engage and spread the inner opposing corners a of the screen frames 26 of the corresponding pairs of stacks 25 and to this end the salient corners of these vertical spreader angle bars project away from each other along the centerline of the sifter body and toward the opposite ends thereof.

Each of these vertical spreader angle bars 50 spreads the inner opposing corners a of the screen frames 26 of the corresponding pair of stacks 25 so as to move the corners b thereof into engagement with vertical indexing or datum angle bars 51 each of which is secured to a corresponding vertical corner angle bar 24 of the sifter frame.

The corners c of each stack of screen frames is clamped against the corresponding vertical corner channel bar 31 of the sifter frame, and to effect such movement of each pair of stacks and also the movement of the corners a thereof against the corresponding vertical spreader angle bar 50, means are provided for simultaneously spreading the corners d of each pair of stacks and also forcing these corners d toward the corresponding vertical spreader angle bar 50, these means being preferably constructed as follows:

The numeral 52 represents generally a hinged plate composed of a pair of vertical angle bars or leaves 53, connected along the edges of their opposing flanges 54 by a suitable number of hinges 55. The other flanges 56 of these vertical angle bars 52 are adapted to be spread to the full line parallel position shown in Figs. 7-9 and also to be swung together about the axis of the hinges 55 to the generally rectangular relation shown by dotted lines in Fig. 8. Each flange 56 has welded to its outer face a vertically elongated abutment or shoulder opposing the corresponding vertical spreader angle bar 50 and shown as being in the form of a tube 58. It will be seen that the flanges 56 and tubes 58 form a pair of vertically elongated abutments projecting from the free edge of each clamping plate 52 and each pair of these abutments forming a vertically elongated notch along the free vertical edge of the corresponding leaf to permit both pairs of abutments to engage the two sides forming the adjacent corner of each stack 26.

The means for expanding the angle bars 53, 53 to the full line position shown in Fig. 8 or contracting them to the dotted line position shown in this figure is shown as comprising a square lug 59 projecting from the outer face of the flange 54 of each of these angle bars 53. By applying a pair of end socket wrenches (not shown) to these lugs, it will be seen that the angle bars 53, 53 can readily be swung about the axis of their hinges 55 to expand or contract the same to the positions shown by full and dotted lines in Fig. 8.

The pair of hinged clamping plates 53, 53 can also be jointly or individually provided with access opening 6i) and which permits access to mechanisms between the two stacks of screens, such as the holddown described in the co-pending application of David Crampton for Sifter, filted February 14, 1950, Serial No. 144,090 now Patent No. 2,653,714.

In addition, the hinged clamping plates 53, 53 are jointly provided at their upper and lower ends with round holes 61 the rim of each of which is beveled to face outwardly, as indicated at 62. This beveled edge or rim on each hole 61 provides a seat for the frusto-conical head 63 of a screw 64. To turn each of these screws, this frusto-conical head is provided with a square extension 65 to provide a wrench head, this wrench head 65 preferably being of the same size as the spreading lugs 59 so that a single end socket wrench can be used on these lugs 59 as well as the heads 65. Each screw 64 screws into a tubular internally threaded socket 66 welded at the end of a rod 68, the opposite ends of each of the rods 68 being threaded and screwing into a threaded opening 69 in the corresponding vertical spreader angle bar 50.

The clamping mechanism forming the subject of the present invention is completed by slidable clamping plates 70 at each outer corner of the main sifter body and each secured to the corresponding vertical corner channel bar 31. As best shown in Fig. 1 these slidable clamping bars 70 are of approximately the same height as the hinged clamping plates 52, and as best shown in Fig. 10 are of channel form in cross section with inner or opposing flanges 71 of slightly greater length than their outer flanges 72. At intervals along its length each slidable clamping bar 70 is provided a horizontal slot 73 receiving a screw 74 having a square head 75 and an integral disk-shaped enlargement 76 which bears against the front face of the corresponding slidable clamping bar 70. Each screw passes through the corresponding vertical corner channel bar 31 and through a nut 77 welded to this vertical corner channel bar. It will therefore be seen that upon tightening the screws 74 by means of an end socket wrench applied to their heads 75, the slidable clamping plates 70 are drawn toward the vertical corner channel bars 31. It will also be seen that upon loosening these screws 74' the slidable clamping bars 70 can be moved horizontally so that their longer flanges 71 either register with the corners c of the stacks 25 of sieve frames to clamp against the same or register with the vertical corner channel bars 31 so as to be out of the way of these stacks of sieves when it is desired to withdraw the screen frames 26.

As with the hinged clamping plate 52, each of these slidable clamping plates 70 can be provided at its lower end with the access opening 78 to permit of access to mechanism, such as a holddown mechanism described in the said Crampton application.

In the operation of a clamping mechanism as above described, assuming that it is desired to remove one or more screen frames 26 from either of the pair of stacks at one end of the sifter, while the sequence of operation is immaterial, the operator can first loosen the slidable clamping plates 70 by applying an end socket wrench to the heads 75 of the screws 74 and unscrew these screws. This releases the longer flanges 71 from engagement with the corners c of the two stacks 25 of screen frames, and since these screws extend through the horizontal slots 73 each of these slidable clamping plates 70 can also be moved sidewise, the operator moving these slidable clamping plates 70 into register with the vertical corner channel bars 31 so that full access is bad to the corners c of each sieve frame 26 of the two stacks 25.

The operator can then apply his socket wrench to the heads of the screws 64. This frees the abutments or tubes 58 of the corresponding hinged plate 52 from engagement with the corners d of the two stacks 25 and by unscrewing these screws 64 far enough the hinge clamping plate 52 can be withdrawn a sufficient distance to permit of its being collapsed to the condition shown by dotted lines in Fig. 8. To so collapse the hinged sections 53, 53 of this hinged plate the operator applies his end socket wrenches to the lugs 59 and turns the sections about the axis of the hinges 55. Upon reference to Fig. 8 it will be noted that by swinging the sections 53, 53 of the hinge plate to the collapsed position shown in dotted lines, the effective width of the hinge plate 52 has been reduced to less than the space between the two stacks 25 of sieve frames. Accordingly full access is had to the two stacks of screen frames and the screen frames 26 can readily be removed and replaced as may be required.

In so replacing the stacks 25 of screen frames 26 at one end of the sifter, the sieve frames are initially placed in engagement with the vertical indexing or datum angle bars 51, that is, the corners b of the screen frames are manually fitted in the corners formed by these angle bars. Also the corners a of these screen frames are manually abutted against the angular faces of the vertical spreader angle bar 50.

After all of the screen frames 26 have been stacked up, the operator can slide the two slidable clamping bars laterally toward each other so that the longer flanges 71 aline with the corners c of the stacks 25 of the screen frames. This lateral movement is permitted by the horizontal slots 73 in these slidable clamping bars. The operator can then apply his end socket wrench to the heads Of the screws 74 and lightly tighten these screws so avenger as to-draw the flanges 71 of thesslidable clamping bars into engagement with these corners 'c.

The operator can then apply his-end socket wrench :to the lugs 59 on the two sections 53 of the hinged clamping plate 52 and swing these two sections :about the axis of their hinges 55 to expand the same toward the full line position shown in Fig. -8. Since the corners d of the two stacks of screen frames at this time have not been forcibly spread apart, this space will-notaccommodate the flanges 56 of these angle bars inthe fully expanded position shown in Fig. 8 and hence, initially, these are expanded to a toeing-in relation in which, however, the abutments or tubes 58 thereof 'aline with and engage the corners d of the two stacks of screen frames. In this toeing-in relation of the flanges 56 the :hinge plates :are manually pushed into engagement with the :corners d of the two stacks of screen frames and the screws 64 are tightened by the application of an end socket wrench to the heads 65 of these screws.

80 tightening these screws 64 operates to draw their frusto-conical heads 63 into engagement with-the beveled seats 62 of the holes jointly provided in the hinged clamping plate 52 and pressure of these conical heads serves to perform two functions. First, this draws the hinge clamping plate 52 toward the vertical spreader angle bar 50 and hence through its abutments or tubes 58 exerts a pressure, indicated by the arrow y, against the corners d of the stacks of screen frames and directed toward the vertical spreader angle bar 50. Since the corners a of the stacks of frames engage the inclined surfaces of the vertical spreader angle bar 50, this force :is converted into a pressure, indicated by the arrow w, against the corners a of the stacks of screen frames and directed toward the indexing or datum angle bars 51. The-second effect .of tightening the screws 64 is to spread the sections or leaves 53 of the hinged plate 52, this spreading resulting from the resistance of the cornersd of the screen frames to-movement of the abutments or tubes 58 of the hinged bar towardthe vertical spreader angle bar:50. This :spreading action of the two leaves or sections 53of the hinge plate 52 creates a force, indicated by the .arrow x, against .the corners d ofthe stacks of screen frames and .toward the vertical corner channel bars 31.

To complete the clamping of the two stacks of screen frames the-screws 74 of the two slidable clamping plates 70 are tightened. In so tightening these :screws 174, the flanges 71 of the slidable clamping plates exert a force, indicated by the arrow z, against the corners .c .of the stacks of screen frames and directed against the vertical indexing or datum bars 51. Accordingly it'will be :seen that each stack of screen frames is clamped :at each of its corners by the corresponding vertical spreader angle bar 50; vertical indexing or datum angle bar #51; vertical corner channel bar 31; slidable clamping plate 170; and tubular abutment 58 and flange 56 of the hinged clamping plate 52, in such manner that pressure is applied against each of the corners a, b, c and d of each screen frame in a direct parallel with each of its sides. Accordingly each stack is securely clamped in position.

In the modification shown in Fig. 3, the'rod 68a, which corresponds to the rod 68 in :the preferred form of the invention, instead of being screwed into the "opening 69a in the vertical spreader angle bar 50a, is :-loosely passed through this hole 69a and is retained by a vertical hinge bar or pin 80 secured to the end of the :rod 681:.

As with the preferred construction, a screw 64a screws into a socket 166a fast to the end of the rod 68a and 'has a frusto-conical head 630 which acts upon the leaves 53a of a hinge plate 52a in the same manner as in the preferred form of the invention. fInstead,'however, of the hinges 55, the leaves 53a of the hinge plate 52a are shown ashinged together by 0-shaped springs 81 which not .only :serve to secured to :the corresponding "leaf 53a :of the hinge plate 52a tby rivets 82. .Since :in other respects the construction andoperation of the modified form of the invention'shown in Fig. .3 .is identical to the preferred form of invention, the detailed description-is.notrepeated and the same reference numerals have been applied and distinguished by the suffix 7a? The vertical hinge bar or pin permits the clamping plates 52a, when retracted, to be swung out of line with either 'of the sieve stacks 25 to permit direct withdrawal of the sieves therefrom. Thus, as shown by dotted lines in Fig. 3, the screw 64a can be unscrewed sufliciently far :and the hinged clamping plates backedoffsufficienttly far to permit .them to be swung, about the axis of the hinge pin 80, either to the right .or left to clear the opposite stacks 2.5 ofsieves and permittheir withdrawal.

A modification .of the :invention is shown in Fig. 4 in which'the invention is :shown .as applied 10 a sifter having .a single stack 25 of :screen frames 26 at each and supported on a platform comprising side bars connected at their ends .to transverse .bars 86. This platform is carried by a pair of inner vertical corner angle bars 88 and 89 which serve-as abutment bars and by a pair of outer vertical corner channel bars 90 and'91. The corner a of the stack of screen frames bears against a vertical plate 92 disposed at anangle 'to the adjacent sides of the stack of screen frames. The corner b of the stack of screen .frames also bearsagainst a vertical plate 93 also disposed ;at an angle :to the adjacentsides of the stack of screen frames.

The corner a of the stack ofscreen frames bears against .an inclined or wedge face 94 along the edge of the flange 1.95 of a channel-shaped slidable clamping bar 96. The other :fiange .98 of this clamping bar is arranged to bear against the face of the vertical corner channel bar 90 of the sifter frame.

-Screws 99 extend through horizontal slots 100 in the web .of the slidable clamping bar 96and each screws into a nut 101-welded to.the vertical corner'channel bar 90.

Similarly the vcorner c of the stack of screen frames :bears against an inclined or wedge face 104 along theedgc of the flange 105 of a channel-shaped slidable clamping bar 106. The other flange 108 of this clamping bar is arranged to bear against the face of the vertical corner channel bar .91 of the sifter frame. Screws 109 extend through Zhorizontal slots 110 in the web of the slidable clamping bar .106 and each screws into a nut'11'1 welded to the vertical corner channelibar 91.

:In removingthe stack 25 of screen frames 26 from the form of theinvention-shown in Fig. 4, all that is necessary is to loosen the screws '99, 109 so as to free the slidable clamping plates 96, .106 whereupon the wedge faces 94, 104 :of these clamping plates can be withdrawn from engagement with the corners d and 0, respectively, of the stack of screen frames. Following this the clamping bars 96, 106 are moved horizontally apart, this being permitted by the horizontal slots 100, 110, through which the screws 99, 109 extend. The screen frames 26 are thereby fully unclamped and rendered available for re moval from the sifter in the manner of drawers.

In replacing the stacks 25 of screen frames, the screen frames 26 are manually pushed against the angle plates 92, 93 so that the corners a and b are initially in abutting relation with the angular faces thereof. The clamping plates 96, 106 are then moved toward each other, this being permitted by the slots 100, 110 for the screws 99, 109, respectively, and their inclined or wedged faces 94, 104 are engaged with the corners d and 0, respectively, of the stack of screen frames. The screws 99, 109 are then tightened and it will be seen that in doing so the stack 23 of screen frames is tightly clamped in each of its corners by forces exerted parallel with the sides of the stack of screen frames. Thus, .on tightening the clamping wedge bar 96,, fits wedge face 94 exerts a force against-the corner d and toward the corner a in the direction of the arrow w so as to cause the corner a to bear against the inclined vertical plate 92. The incline of this vertical plate, in turn, provides a force in the direction of the arrow x toward the vertical inclined plate 93. The inclined face 94 of the clamping plate 96, in turn, imposes a force on the corner d in the direction of the arrow y toward the clamping plate 106. Upon tightening the screws of the clamping plate 106, a force is created, indicated by the arrow z, toward the vertical inclined plate 93. It will therefore be seen that each corner of the stack of screen frames is securely clamped against the abutting surfaces by forces exerted in a direction parallel with the adjacent sides of the screen frame against that corner. It will further be seen that the essential distinction between this form of the invention and the prefererred form is that either of the vertical inclined plates 92 or 93 can be regarded as the indexing or datum bar or abutment, the stack being, to a certain extent, free to find its final location. However this in no way detracts from the security with which the stack is held.

While the invention is shown as embodied in a four section sifter and also, in Fig. 4 as adaptable to a two section sifter, it is obvious that it can also be embodied in a six or more section sifter.

From the foregoing it will be seen that the present invention provides a very simple mechanism for securely clamping stacks of screens to the frame of a gyratory sifter and holding the stacks reliably in position against the forces generated in the high speed gyration of the shifter. It will further be seen that the clamping mechanism is rendered operative or inoperative by the simple expedient of tightening and loosening a few screws. It will also be noted that when rendered inoperative the clamping mechanism exposes the entire face of the stack of screens so that they can be readily withdrawn, rearranged, or replaced by other frames. It will, also, be particularly observed that at all times the parts of the clamping mechanism are attached to the sifter frame so that there is no danger of these parts becoming lost or injured, and also so that there is no requirement for carefully fitting a detached part to the anchoring part of the sifter frame.

I claim:

1. In a sifter including a movable platform adapted to support a stack of rectangular screen frames, the combination therewith of means for clamping said stack from the sides thereof to said platform, comprising at least one vertical bar fastened in fixed relation to said platform and engagable with adjacent vertical sides of said stack along one corner of said stack, a vertical clamping plate engagable with the corner of said stack diagonally opposite said one corner and in adjustable relation to said platform to exert pressure on said opposite corner in directions toward each of the corners of said stack intermediate said one corner and said opposite corner, a vertical bar fastened in fixed relation to said platform and having a generally fiat vertical angular face engageable with one of said intermediate corners and arranged at an acute angle to the adjacent sides of said stack whereby the pressure exerted by said clamping plate through said stack against said angular face is transmitted by said angular face against said one vertical bar, and a second clamping plate engageable with the intermediate corner opposite said angular face and adjustable relative to said platform to exert pressure against its corner of said stack in a direction toward said one vertical bar.

2. In a sifter including a movable platform adapted to support a stack of rectangular screen frames, the combination therewith of means for clamping said stack from the sides thereof to said platform, comprising a vertical indexing bar fastened in fixed relation to said platform and engageable with adjacent vertical sides of said stack along one corner of said stack, an abutment bar fastened in fixed relation to said platform adjacent each corner of said stack intermediate said one corner of said stack and the corner diagonally opposite therefrom, one of said abutment bars being provided with a generally vertical angular face engageable with the adjacent corner of the stack and arranged at an acute angle to the adjacent sides of the stack thereby to transmit pressure exerted against it from along one of said adjacent sides in a direction along the other of said adjacent sides, a vertical clamping plate connected to the abutment bar opposite said abutment bar having said angular face and arranged to exert pressure on its corner of said stack toward said indexing bar, a second vertical clamping plate adjustably secured to said platform to engage said diagonally opposite corner of said stack, and means arranged to move said second vertical plate in directions both toward said angular face and toward said abutment bar connected with said first clamping plate thereby to exert pressure on said diagonally opposite corner of said stack in corresponding directions.

3. In a sifter including a movable platform adapted to support a stack of rectangular screen frames, the combination therewith of means for clamping said stack from the sides thereof to said platform, comprising a vertical indexing bar fastened in fixed rotation to said platform and engageable with adjacent vertical sides of said stack along one corner of said stack, a pair of clamping plate leaves arranged at the corner of said stack diagonally opposite said indexing bar and connected with each other to swing about a common vertical axis and to be extensible into planar relation with each other, the apex of said leaves, in the collapsed condition thereof, being directed away from one of the corners of said stack intermediate said indexing bar and clamping plate leaves, a flange on one of said leaves and formed to engage the adjacent portions of the two sides of said stack forming the corner diagonally opposite said first corner, means restraining the expanding movement of the other of said leaves whereby pressure applied horizontally to the apex of said clamping plate leaves in a partly contracted condition exerts pressure on said diagonally opposite corner in directions parallel with said two sides, a vertical bar fastened in fixed relation to said platform at said one of the corners of said stack and having a vertical face engageable with one of the other corners of said stack and angularly disposed at an acute angle with reference to the adjacent sides of said stack of screen frames, whereby pressure derived from said clamping plate leaves is transmitted toward said indexing bar, a vertical abutment bar fastened in fixed relation to said platform and engageable with the corner of said stack diagonally opposite said angularly disposed face, and a clamping plate on said vertical abutment bar and arranged to exert pressure on the corresponding corner of said stack in a direction toward said vertical indexing bar.

4. In a sifter including a movable platform adapted to support a stack of rectangular screen frames, the combination therewith of means for clamping said stack from the sides thereof to said platform, comprising a vertical indexing bar fastened in fixed relation to said platform and engageable with adjacent vertical sides of said stack along one corner of said stack, a pair of clamping plate leaves arranged at the corner of said stack diagonally opposite said indexing bar and connected with each other to swing about a common vertical axis and to be extensible into planar relation with each other, the apex of said leaves, in the collapsed condition thereof, being directed away from one of the corners of said stack intermediate said indexing bar and clamping plate leaves, a flange on one of said leaves and formed to engage the adjacent portions of the two sides of said stack forming the corner diagonally opposite said first corner, means restraining the expanding movement of the other of said leaves whereby pressure applied horizontally to the apex of said clamping plate leaves in a partly contracted condition exerts pressure on said diagonally opposite corner in directions parallel with said two sides, a vertical bar fastened in fixed relation to said platform at said one of the corners of said stack .and having a vertical face engageable .with one of the other corners of said stack and angularly disposed at an acute angle with reference to the adjacent sides of said stack of screen frames, at horizontal screw having one end threadedly connected with said bar having said angularly disposed face and having a headed end extending through apertures in said apex of said hinged leaves whereby tightening said screw applies pressure horizontally to the .apex of said leaves and this pressure is transmitted by said angularly disposed face toward said indexing bar, a vertical abutment bar fastened in fixed relation to saidplatform and engageable with the corner of said stack diagonally opposite said angularly disposed face, and a clamping plate on said vertical abutment bar and arranged to exert pressure on the corresponding corner of said stack in a direction toward said vertical indexing bar.

5. In a sifter including a movable platform adapted to support two spaced stacks of rectangular screen frames, the combination therewith of means for clamping each of said stacks from the sides thereof to said platform, comprising a pair of vertical indexing bars -fastened in fixed relation to said platform and engageable with companion corners of a corresponding stack remote from the space between said stacks, a pair of clamping plate leaves arranged at the corners of said stacks opposite said companion corners and connected with each other to swing about a common vertical axis and to be extensible into planar relation with each other, the apex of said leaves, in the collapsed condition thereof, being directed away from the mutually adjacent corners of said stacks which are arranged intermediate said indexing bars and clamping leaves, a flange remote from said axis on each of said leaves and each formed to engage the adjacent portion of the two sides of a corresponding stack forming the corner thereof diagonally opposite said first corner, a vertical spreader bar fastened in fixed relation to said platform .at the end :of the space between said stacks opposite said clamping plate leaves and having vertical faces each engageable with .the said mutually adjacent corners .of said stacks at an acute angle to the adjacent sides of each of said stacks whereby pressure derived from said clamping plate leaves is transmitted by said vertical faces toward each of said indexingbars, means arranged to apply pressure horizontally to the apex of said clamping plate leaves while in a contracted condition and in a direction toward said spreader bar to exert pressure on said diagonally opposite corners of said stacks in directions parallel with said two sides of said stacks, a pair of vertical abutment bars fastened in fixed relation tn said platform and each engageable with the corner of a corresponding stack diagonally opposite said spreader bar, and a clamping plate on each of said vertical abutment bars and arranged to exert pressure on the corresponding stack corner in a direction toward the corresponding vertical indexing bar.

6. In a sifter including a movable platform adapted to support two spaced stacks of rectangular screen frames, the combination therewith of means for clamping each of said stacks from the sides thereof to said platform, comprising a pair of vertical indexing bars fastened in fixed relation to said platform and engageable with companion corners of a corresponding stack remote from the space between said stacks, a pair of clamping plate leaves arranged at the corners of said stacks opposite said companion corners and connected with each other to swing about a common vertical axis and to be extensible into planar relation with each other, the apex of said leaves, in the collapsed condition thereof, being directed away from the mutually adjacent corners of said stacks which are arranged intermediate said indexing bars and clamping leaves, a flange remote from said axis on each of said leaves and each formed to engage the adjacent portions of the two sides of a corresponding stack forming the cornerthereof diagonally opposite said-first corner, a vertical spreader bar fastened in fixed relation to said platform at the end of the space between said stacks opposite said clamping plate leaves and having vertical faces each engageable with the said mutually adjacent corners of said stacks at 'an acute angle to the adjacent sides of each of said stacks whereby pressure derived from said clamping plate leaves is transmitted by said vertical faces toward each of said indexing bars, a horizontal screw having one end threadedly connected with said spreader bar and having a headed end extending through apertures in said apex of said hinged leaves whereby tightening said screw applies pressure horizontally to the apex of said leaves to exert pressure on said diagonally opposite corners of said stacks in directions parallel with said two sides of said stacks, a pair of vertical abutment bars fastened in fixed relation to said platform and each engageable with the corner of a cor responding stack diagonally opposite said spreader bar, and a clamping plate on each of said vertical abutment bars and arranged to exert pressure on the corresponding stack corner in a direction toward the corresponding vertical indexing bar.

7. In a mechanism for clamping two spaced stacks of rectangular screen frames from the sides thereof on the platform of a sifter, .an expansible clamping plate adapted to fit the adjacent corners of said two stacks at one end of the spacer therebetween, comprising a pair of vertically elongated clamping plate leaves, means hingedly connecting said clamping plate leaves to swing about an axis extending along opposing vertical longitudinal edges, a pair of vertically elongated abutments projecting from the other vertical longitudinal edge of each of said clamping plate leaves and each pair of said abutmentsbeing formed to provide a vertically elongated notch along said other vertical edge of the corresponding leaf to permit both pairs of abutments to engage the two sides forming said adjacent corner of each of saidstacks, and means arranged to move said clamping plate leaves with reference to each other about said axis.

8. In a mechanism for clamping two spaced stacks of rectangular screen frames from the sides thereof on the platform of a sifter, an expansible' clamping plate adapted to fit the adjacent corners of said two stacks at one end of the space therebetween, comprising a pair of vertically elongated clamping plate leaves, means hingedly connecting said clamping plate leaves to swing about an axis extending along opposing vertical longi tudinal edges, and abutments projecting from the other vertical longitudinal edges of said clamping plate leaves and each formed to engage the two sides forming said adjacent corner of each of said stacks, said clamping plate leaves being jointly apertured along said opposing edges to receive a draw screw arranged to move said clamping leaves with reference to each other about said axis.

9. In a mechanism for clamping two spaced stacks of rectangular screen frames from the sides thereof on the platform of a sifter, an expansible clamping plate adapted to fit the adjacent corners of said two stacks at one end of the space therebetween, comprising a pair of vertically elongated clamping plate leaves, means hingedly connecting said clamping plate leaves to swing about an axis extending along opposing vertical longitudinal edges, a vertical flange projecting laterally from the other longitudinal edge of each of said leaves into the space between said stacks and to engage the opposing faces of said stacks, a vertical abutment on the sides of each of said flanges remote from each other and arranged to engage the faces of said stack meeting said opposing faces to form said adjacent corners, and means arranged to move said clamping plate leaves with reference to each other about said axis.

10. In a sifter including a movable platform adapted to support a stack of rectangular screen frames, the combination therewith of means for clamping said stacktfrom the sides thereof to said platform, comprising a plurality of vertical abutments movable with said platform and each arranged at a corresponding corner of said stack, the abutments at the corners of said stack formed by a common side of said stack having generally fiat vertical faces angularly disposed with reference to said common side and engaging the adjacent corners of said stack at an acute angle whereby pressure imposed by either of said corners against its said angularly disposed face from a direction perpendicular to said common side is transmitted in the direction of said common side to the other angularly disposed face, a clamping plate secured to each of the other two abutments and means mounted on said platform adjacent each of said clamping plates and arranged to force each of said clamping plates to exert pressure on the adjacent corner of the stack toward each other and also toward the adjacent one of said angularly disposed faces.

11. In a sifter including a movable platform adapted to support a stack of rectangular screen frames, the combination therewith of means for clamping said stack from the sides thereof to said platform, comprising a vertical indexing bar fastened in fixed relation to said platform and engageable with one corner of said stack, a pair of clamping plate leaves connected with each other to swing about a common vertical axis and to be extensible into planar relation with each other, a flange on one of said leaves and formed to engage the adjacent portions of the two sides of said stack forming the corner diagonally opposite said first corner, means restraining the expanding movement of the other of said leaves whereby pressure applied horizontally to the apex of said clamping plate leaves in a partly contracted condition exerts pressure on said diagonally opposite corner in directions parallel with said two sides, a vertical bar fastened in fixed relation to said platform and having a vertical face engageable with one of the other corners of said stack and angularly disposed at an acute angle with reference to the adjacent sides of said stack of screen frames, a horizontal screw having one end hingedly connected with said bar having said angularly disposed face to swing about a vertical axis and having a headed end extending through apertures in said apex of said hinged leaves whereby tightening said screw applies pressure horizontally to the apex of said leaves and this pressure is transmitted by said angularly disposed face toward said indexing bar, a vertical abutment bar fastened in fixed relation to said platform and engageable with the corner of said stack diagonally opposite said angularly disposed face, and a clamping plate on said vertical abutment bar and arranged to exert pressure on the corresponding corner of said stack in a direction toward said vertical indexing bar.

12. In a sifter including a movable platform adapted to support a stack of rectangular screen frames, the combination therewith of means for clamping said stack from the sides thereof to said platform, comprising a plurality of vertical abutments movable with said platform" and each arranged at a corresponding corner of said stack, the abutment at one or more corners other than opposite corners of said stack having a generally flat vertical face angularly disposed with reference to both adjacent vertical faces of said stack and engaging said one corner of said stack at an acute angle in a horizontal direction whereby pressure imposed horizontally against said stack along either of said adjacent vertical faces in the direction of said one corner is translated into movement of said one corner along said generally flat vertical angularly disposed face which in turn is transmitted by said flat vertical angularly disposed face into force against the other of said adjacent vertical faces, means adjacent to at least one other corner of said stack for creating such a pressure, and means at at least one more corner of said stack for limiting said movement of said one corner thereby to convert said pressure into a clamping force securing said stack to said platform.

References Cited in the file of this patent UNITED STATES PATENTS 287,597 Wehrer Oct. 30, 1883 726,073 Konegen Apr. 21, 1903 758,907 Fraser May 3, 1904 FOREIGN PATENTS 24,106 Austria Dec. 15, 1905 26,340 Great Britain Nov. 16, 1912 165,967 Germany June 3, 1904 253,954 Germany Nov. 21, 1912 295,419 Great Britain Aug. 9, 1928 296,528 Germany May 26, 1916 357,545 Germany Aug. 26, 1922 

